I'm trained to clear a house.
... with a few other members of a team, and only in a situation that requires it. With my living arrangements, this would be unnecessary.
In my mind, this is more of a "war" situation, and I'd be taking a defensive position.
For me, I'll stick to holing up in the bedroom, armed with my 9mm w/ spare mags and a turned-off flashlight. I'd get my girlfriend in a corner with as much cover as possible and have her dial 911 on one of our cell phones, alerting the police of the situation and our position in the apartment.
I'd retain the element of surprise as much as possible. If it's obvious that the home invaders know I'm in there, I'd yell that I'm armed, the police are on their way, and if that door opens an inch, they're dead (btw, I always keep my bedroom door locked, as well as the entrance doors to my apartment. I spent too many college years living in an apartment building where some drunk would accidentally walk into my living room looking for someone that lived on an entirely different floor).
However, there's a window in my bedroom. If I was awakened by an intruder breaking in through the window, he'd be dead before his foot touched the carpet.
I think keeping doors/windows locked is a simple, yet integral beginning to safety. Keep as many locked doors between you and the intruder as possible. That way, no one can "slip" into your house without audible warning -- glass breakage, kicking in a door, etc. You, or, better yet, your dog (wish I could have one here) will become alert to the situation at hand.
CZ 75B 9mm Duo Tone, Ruger 22/45 5.5" Bull Barrel .22, Savage Mark II .22LR, M44 Mosin Nagant, Remington 870 12ga Super Mag